1. Field of the Invention
The present invention relates generally to noise elimination schemes, and more particularly, to noise elimination devices for avoiding interference of high frequency noises within telephones or associative exchange modules.
2. Description of the Prior Art
In recent years, wireless radiotelephone communication systems have been developed which include a city-wide telepoint system employing mobile telephone handset units, e.g., portable or handheld radiotelephone transceivers that can access the public switched telephone network via any accessible base unit within a defined geographical coverage area. As such mobile radiotelephone transceivers are becoming more widely used with the coexisting telephone network, the prior established stationary telephones and associated switch or exchange modules therein encounter more frequently a problem in that noises are induced by such transceivers to adversely affect communications in the stationary telephones. Because the transceivers are designed to operate at specific frequencies high enough to go beyond 800 MHz (typically, in a range of 1 to 2.5 GHz), high frequency components may possibly induce noises, which will enter or "invade" the prior established telephones and/or associated exchange modules by way of communication lines. While the telephones and exchange modules come with one or more general purpose or common mode choke coils for protection against unwanted mixture of high frequency noises, the choke coils are designed with no consideration aimed at protection from such high frequency noises as induced by outside radiotelephone transceivers.
The presently available choke coils generally employ either windings increased in the number of turns or windings wrapped around a core to form a multi-layered configuration. This means that the resulting stray capacitance between adjacent ones of turns of winding portions remains relatively large; for example, as large as 5 picofarads (pF). This results in the impedance decreased below 50 ohms (.OMEGA.) at a frequency of 1 gigahertz (GHz) making it impossible to remove or eliminate such high frequency noises.